Droning noise/Harmonic sound

[tmontague]

usually would point to a bad wheel bearing...since you changed all of those and I'm assuming checked that they were good before you installed them then I'm not quite sure. Someone else will chime in I'm sure with an idea.

In regards to your coolant...ya you're going to want to deal with that asap and before you worry about a droning noise. If your coolant reservoir is constantly going empty then you have a pretty severe leak somewhere. It will leave a trail of white/pink crust (assuming you're using toyota coolant) where it's leaking so get under the car and nail down where your coolant is going.

If you have a pinkish streak running back to front under your hood just above where the water pump is then yeah you're pump is bad. Get a lifetime warranty one from parts source, not the cheapest but worth it if you change it yourself.

I wouldn't be driving the car around too much with a constantly emptying overflow reservoir

EDIT* make sure the droning isn't happening on newly paved roads only during your trip. This commonly happens until pavement is worn down a bit